The following account of the prior art relates to one of the areas of application of the present application, hearing aids.
Real-ear-to-coupler difference (RECD) is defined as the difference in dB as a function of frequency between a sound pressure level (SPL) measured in the real-ear (of the particular user) and in a standard coupler (e.g. 2 cm3, often written as 2-cc, or an IEC 711 coupler, etc.) acoustic coupler, as produced by a transducer generating the same input signal in both cases. When measuring the real-ear-to coupler difference the measured low frequency (LF) gain varies due to small variation in the ear-mould placement. The actual RECD may therefore vary every time the ear mould is inserted, making it difficult to provide the correct low frequency amplification.
US2007217639A1 deals with a real ear acoustic coupling quantity representative of the acoustic coupling of a hearing instrument to the user's ear or an anatomical transfer quantity is obtained from a transfer function representative of an acoustic transfer from the receiver to the outer microphone such as a signal feedback threshold gain. The obtained quantity may be used for setting a fitting parameter of the hearing instrument, for example a gain correction.